I've been playing bass for under two decades. During the last four years I've played thru Hartke cabs (alluminium cones). Nowadays I use a 4.5XL (4x10" + horn) and a 215XL (2x15"), both front ported cabs. But I've grown a little tired of alluminium and plan on going back to paper cones. The thing is I love this configuration and I love these two boxes (solid construction, nice look) and would like to just replace their speakers. I've been doing some experiments with Eminence Betas in WinISD, trying to aproach the best tuning values possible. At this point I have some questions regarding my project:

1) Eminence Betas are the ones with best compromise (SPL/response/excursion) in the low end. Are they a good choice or should I definitely go some other route?

2) Either Betas are the choice or not, I see lots of bass cabs tuned lower than Fs. Should I tune the cabs below Fs? Much lower? I play 5-string bass (dropped low A, at 27.5Hz). I've never had problems reproducing it with my Hartkes (rated response starts at 30Hz -which I doubt, I believe that's just the -10dB point-). I want good sub low, but avoiding boomyness or muddyness (I definitely need articulation).

3) If I tune too low I may ran out of excursion soon (that's what I see in WinISD), am I right about this?

4) (EDIT) Should I worry about the excursion peaks I get in WInISD at around 70Hz (just for the 2x15", I also have a similar peak on the 4x10" but I plan on using it hi-passed at 100Hz)?

As an additional comment I plan on having them both work at 4ohms, driven with a 2x450W@4ohms power amp (1 channel for each cab).

Just need to know if I'm taking the right path here or missing it completely. Thanks so much for your help!

I know that you need quality drivers for your bass but with that much power in your hands, you should definitely look in the direction of HT subwoofer drivers. At least to compare with the Betas. Especially since you use 10 inches drivers to take the midbass.

I can get Eminence drivers at very reasonable prices here, from a german on-line store (from which I alredy bought gear a couple of times) so I'd try to stay within Eminence whole line. Peerless local distributors charge a lot on these drivers, so unless I'm finding some cheaper on-line store (which I'm hjaving a hard time finding) I'm affraid I can't count on the Peerless drivers.

Betas can be good for my 4x10" (hi-passed) solution, but i definitely will get farting around 70Hz on the 2x15" (I assume 7mm excursion when Xmax is 4mm translates un noticeable, non "musical", distortion, am I right?) no matter if I tune at Fs, lower or even higher. The problem is, using Betas on both, according to Eminence's specifications, I could get similar SPLed cabs. So I also have to be careful not to end up having a too "quiet" 2x15" cab if I change my options on the 15"s. I'll keep on searching. By the way, I absolutely love Peavey's Black Widow 15"s. And I've seen (and played, and loved) several 2x15 Black Widow equipped Peavey cabs. Is it too bad of an idea to think of Black Widows?

Thanks again and sorry to be such a pain in the a$$ due to my inexperience!